The invention relates to a leaf spring made of a fiber composite material having integrated bearing eyes according to the disclosure and to a method for producing the same.
Leaf springs having end-situated bearing eyes are known per se and are used, for instance, in vehicles, where they serve to cushion the body of the vehicle from the chassis. Conventionally, leaf springs consist of several layers of narrow metal plates, which are stacked one upon the other and are held together by means of holding elements. Leaf springs made of composite materials have also however been proposed.
An earlier leaf spring construction consists of a plurality of composite components which are arranged one above the other and are connected to one another by retaining clips to form the leaf spring. Each of these composite material layers consists of an upper and a lower metallic sheet metal strip, between which a rigid plastics core is disposed. On at least one axial end, this leaf spring has a bearing eye integrated thereon, which bearing eye is formed by bending over and axially leading back the sheet metal strips of the topmost composite material layer to the axial middle of the leaf spring. This is realized such that the upper sheet metal strip of the composite material layer is guided around a circular sleeve in the direction of the lower sheet metal strip, while the lower sheet metal strip of this composite material layer, with the rigid plastics material inserted therebetween, is likewise guided around the sleeve, yet is deposited on the top side of the upper sheet metal strip. It is regarded as a drawback with this leaf spring that its structure consists of two different materials, and that the comparatively complicated wrapping of the bearing eye sleeve is laborious and therefore increases the production costs. Moreover, it is not possible to ensure that the rigid plastics core, disposed between the metal strips, of each individual composite material layer will withstand the prolonged alternating loads to which a leaf spring in a vehicle is operationally exposed.
Against this background, an object of the invention is to provide a leaf spring for a vehicle which can be cost-effectively produced and has high resistance to prolonged alternating load. This leaf spring should be produced from a non-metallic material and have on at least one of its axial ends a bearing eye integrated into the leaf spring. Moreover, a production method by which such a leaf spring can be cost-effectively produced shall be described.
The achievement of this object is derived, for the production method, from the features disclosed and claimed herein. Described herein is a leaf spring which achieves the device-related object. The disclosure and claims describe preferred embodiments of the invention.
The invention is based on the insight that the object can be achieved if the leaf spring is produced fully from a fiber composite material, namely from a fiber composite material, for instance consisting of prepreg strips laid one on top of the other in layers. Prior to the setting of the prepreg strips, the axial ends of the stack of the prepreg strips are bent in the shape of a circle, to form the at least one bearing eye, in the direction of the middle of the crude leaf spring and are connected to the fiber composite material which is farther away from the axial end. Next the crude leaf spring is hardened in a suitable mold, with the application of a setting temperature and setting pressure.
With the term “prepreg” is used to denote an intermediate product which consists of at least one layer of synthetic fibers impregnated with a synthetic resin. The synthetic fibers can be present in the prepreg as a woven fabric or as unidirectionally oriented fiber strands. The prepreg strips are cut to a predefined circumferential geometry. In the construction of the workpiece to be made up of this material, the synthetic resin is not yet hardened.